1. Field of the Invention
The present invention relates generally to a window blind and, more specifically, to a window blind control structure for use in a window blind to control the elevation and tilting angle of the blind slats.
2. Description of the Related Art
A conventional window blind is generally comprised of a headrail fixedly located on the top side of the window, and a blind body suspended from the headrail and controllable by an external force to change its window shading status.
Conventional window blinds may have the lift cord and tilt cord exposed to the outside or arranged in a hidden status. A window blind with exposed lift cord and tilt cord has the lift cord and the tilt cord respectively suspended from the left and right ends of the headrail for pulling by the user to adjust the elevation or tilting angle of the blind slats. Because the lift cord and the tilt cord are exposed to the outside and accessible to children, an accident may happen when a child playing with the lift cord or tilt cord for fun.
Various window blinds with hidden cord members have been disclosed, and have appeared on the market. There is known a window blind with hidden cord members which uses spring means to keep the blind slats in balance and to hold the blind slats and the bottom rail in position after an adjustment of the window blind by the user. There is known another design of window blind with hidden cord members, which uses the tension force of a positioning cord member to support the bottom rail in position after an adjustment of the window blind by the user. The use of spring means of positioning cord member cannot eliminate the problem of elastic fatigue. When the problem of elastic fatigue occurred, the spring means or positioning cord member can no longer support the bottom rail accurately in position. There is also known a window blind, which uses an operation rod and a linking mechanism to substitute for a lift cord for blind slats lifting control. A similar design is shown in French Patent Publication No.2692002. This window blind design eliminates the drawbacks of the aforesaid conventional window blinds with hidden cord members. However, this design is used for controlling the elevation of the blind slats only. It cannot control the tilting angle of the blind slats. For controlling the tilting angle of the blind slats, an additional tilting rod and tilting transmission mechanism should be provided. The arrangement of the additional tilting rod and tilting transmission mechanism greatly complicates the structure of the window blind. Because lifting and tilting of the blind slats are separately controlled, the operation is inconvenient.